(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Calculate the force of magnetic attraction between the northern and southern hemispheres of a uniformly charged spinning spherical shell, with radius R, angular velocity ω and surface charge density σ.

2. Relevant equations(1/μ) *

Maxwell Tensor : T_{m}=((B*n)B - (1/2)*B^{2}n)(2/3)*μσRω

B_in =*zμm

B_out =/(4πr^{3}) * (2cosθr +sinθθ)m = (4/3)*πR

where^{3}(σωR)

3. The attempt at a solution

I do see in my solution that :

1-We use a surface consisting of the entireequatorial plane, CLOSING IT with a hemispherical surface at infinity where (since the field is zero out there) contribution is zero.

for r>R :

B = μm/(4πr^{3})θ =- μm/(4πr^{3})z (Why ?! )We have a equatorial circular disk. We use B inside and da = rdrdφ. Direction is in z-axis!

2-

I don't want the solution because I already have it but MY QUESTIONS are :

A) How should think and imagine this spheres ?!

Should I think like this and use those formulas :

B) Why we do write B = μm/(4πr^{3})θ =- μm/(4πr^{3})z

Why is θ =-z in this case ?! I dont get it !

I know the rest. That is just integrating

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# Homework Help: Force of magnetic attraction between hemispheres

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